Resistive, inductive and magnetic solutions are known for measuring current. Resistive solutions are distinguished by a large measurement range combined with a high degree of measurement accuracy at low currents, but can be galvanically isolated only by complicated signal processing and cause interference under certain circumstances owing to a voltage drop at peak loads. Inductive methods utilize the law of induction, for example, in so-called Rogowski coils or current transformers, and are therefore only compatible with alternating current without complicated integrative circuitry. The strength of a magnetic field which is generated by a conductor through which current flows is measured in the case of magnetic current sensors. Therefore, these solutions are compatible with alternating current and direct current.
The magnetic field probes used may be, in particular, Hall sensors, AMR sensors (AMR, “anisotropic magnetoresistance”), GMR sensors (GMR, “giant magnetoresistance”) and fluxgate probes. In order to amplify the magnetic field at the measurement location and to shield from external fields, ferromagnetic cores are generally used in this case, but said ferromagnetic cores, on account of the hysteresis in the case of so-called open-loop methods, limit the degree of measurement accuracy at low currents owing to the residual magnetization in the material. In so-called closed-loop methods, the magnet probe is used to keep the magnetization in the core at zero by means of a control group and an additional coil around the core. The measurement accuracy at low currents improves as a result. When using sensitive field strength-sensitive AMR or GMR elements, only measurement in a restricted current range would be possible with an open-loop design since the sensors do not have a large dynamic range on account of the saturation of the elements.